Manufacture of mercerized cellulose products



Patented Apr. 23, 1935 UNITED STATES PATENT 'OFFICE MANUFACTURE OF MERCERIZED CEL- LULOSE PRODUCTS of Maine No Drawing. Application May 2, 1931, Serial No. 534,708

10 Claims.

This invention relates to the manufacture of mercerized cellulose products into which cellulose fiber of the character of chemical wood pulp sheets of interfelted fibers fabricated on machinery of the papermaking type. While it is practicable to mercerize sheets of interfelted fibers (and this has been done in viscose manufacture), nevertheless it is still more practicable and economical to mercerize bulk fiber, such as chemical wood pulp, as large quantities of stock can be handled in apparatus of the simplest kind.

Again, the mercerized bulk fiber can be easily washed in countercurrent washing machines,

such as used in the pulp industry, which efiect a separation of the mercerizing liquor for re-use, without great dilution from the mercerized fiber. Indeed, in a mill producing chemical wood pulps, the standard equipment existing therein, including tanks, pumps, pipes, washers, etc., is serviceable for mercerizing vast quantities of such pulps by treating them as they flow in aqueous suspension through the pulp mill. They may be mercerized and washed at any suitable stage in the pulp mill, for instance before or after bleaching; or the mercerizing treatment may be combined with a bleaching operation.

In accordance with the present invention, cellulose fiber in bulk condition, and more particularly chemical wood pulp, is mercerized and then washed in such condition, whereupon the rnercerized and washed pulp is formed into sheets of interfelted fiber on machinery of the papermaking type. By fabricating the sheets from bulk, mercerized fiber, not only am I able to benefit by the economic advantages accruing from mercerizing the bulk fiber, but the resulting sheets are possessed of high porosity and absorbency and are remarkably soft. These characteristics are present in the resulting sheets by virtue of the quality of the mercerized fiber itself; and can be supplemented by forming the sheets and drying them without the use of pressrolls or other devices relied upon in conventional papermaking practice to condense the nascent, wet webs of interfelted fiber. The webs may, in fact, be formed and dried directly on a foraminous carrier or 'wire,-precaution being taken to avoid stretching or other stress of the webs such as would tend to rupture them. The sheet product of the present invention, although of low tensile strength, is eminently adapted for use as a base or foundation for impregnation with 1atex, rubber solution, or the like, in the production of artificial leathers. It may also serve as a carrier sheet for other impregnating or bonding media of a tion, like that of latex or rubber solution, is to impart such qualities as strength, toughness, and water resistance to the sheet after impregnation and drying. A most important use for the product of the present invention is in the field of cellulose derivative production, such as the Xanthate, nitrate, and acetate; Its sheet form means that it can be stored, packed, and shipped economically. The low solution viscosity of the fibers and their mercerized state make for smooth esterification; and the high alpha cellulose content of the mercerized fibers leads to derivatives of the highest quality. In this connection, it is to be observed that the mercerizationof the pulp may be readily conducted under conditions to produce a mercerized product which, after washing, has an alpha cellulose content upwards of about 96% (frequently 98%) and a solution viscosity of less than 0.6, but in some instances, however, the mercerizing steps may be performed without drastically lowering the solution viscosity of the fiber, as whenthe product is to serve as a carrier sheet for impregnating media. For instance, by using a mercerizing liquor for a sufficient period of time at room temperature, chemical wood pulp, such as sulphite, may be converted into the desired product. The use of mercerizing liquors at low temperatures, say, distinctly below freezing, facilitates the attainment of the desired product; and the addition of oxidizing agents, such as hypochlorites or permanganates, to the bleaching liquor promotes the reduction of the solution viscosity of the fiber to the desired low value, i. e., to a solution viscosity less than 0.6. Such a product can be directly and completely xanthated by treatment with the appropriate amount of caustic soda and carbon bisulphide to produce the xanthate, which means that the usual long period of aging the so-called soda cellulose has been dispensed with. When unbleached chemical wood pulp, such as sulphite, is used as the starting material and the mercerized product is intended for making derivatives, such pulp is bleached before or after the step of mercerization. Or sufficient bleach,

such as hypochlorite, is added to the mercerizing liquor to exert'the desired decolorizing action, in which case the bleach, as already indicated, is distinctly favorable to a reduction in the solution viscosity of the fiber to the low value desired.

wide variety, whose primary func In order to attain sheets of uniform formation or texture from the bulk, mercerized fiber on machinery of the papermaking type, one must bear in mind the tendency of mercerized fiber to clot or bunch, and thus to give rise to sheets of markedly irregular density and thickness. In other words, one must guard against the propensity of mercerized' fiber to deposit as wild sheets on papermaking machines. In order to overcome this difficulty, the mercerized fiber should be beaten and/or jordaned or otherwise mechanically treated, so as to individualize or disassociate the fiber units and thereby to produce a homogeneous suspension, even though in so doing the fibers are drastically cut or short ened and the resulting sheet is made even more tender than it would otherwise be, owing to the inherent, non-hydratable character of the mere cerized fiber. The beating action to which the fiber is subjected may to advantage be supplemented by the action of a Jordan or refining engine, whereupon the fiber may be run oil on a 'papermaking machine, into sheets of the desired basis weight and compactness. Thus, the sheets may be as light as pounds or as heavy as 200 pounds. basis weight. Their compactness may range from to 70, although calendering treat- :ment may increase the compactness to about 100. The basis weight is the weight of 480 sheets,"

24 x36 inches. Compactness is determined by dividing the basis weight by. the product of the thickness in inches times 100. For instance, a sheet having a basis weight of 40 pounds and a thickness of 0.004 inch possesses a compactness .of 100. Such sheets lack those qualities, including strength, tear resistance, folding endurance, etc., demanded in papers intended for use as such, but they answer the requirements sought for in the other important spheres for which they are designed. The sheets because of their softness and resiliency lend themselves to embossing and in some-cases may first be impregnated with such media as nitrocellulose lacquers, rubber latex or-rubber solutions, casein glues, or the like and then embossed. Or the steps of impregnation and embossing may be reversed-in order. It may be additionally mentioned that other factors conducive to uniform sheet formation may ice-availed of in the production of my product, such as the use ofa papermaking machine having a Fourdrinier wet end, the delivery of the mercer-ized pulp to the machine as a highly dilute suspension,

and the use of hot wateras the suspension vehicle. The use-of hot water-evidently tends to set incipiently gelatinized cellulose which may be generated'on the fiber as a result of mercerization, and thus to inhibit sticking and launching of fibers.

'I am not unmindfulof my Patent No. 1,700,596, issued January 29, l929, wherein I have disclosed the use of a mixture of mercerized andunmercerized cellulose fiber for forming paper'sheets. The product of the present invention, however, is made wholly from bulk, mercerized fiber, and hence represents a uniform product which can undergo uniform esterification. For instance, when mercerized to sufficiently low solution viscosity, it may be xanthated directly, without leaving unxanthated fibers or whiskers,- whereas a portion of the fibers, if :unmercerized, being of; comparatively high-solution viscosity, would remain unxanthated, unless ageing were resorted to,'as in the usual viscoseprocess. The reduction in fiber length ensuing from. beating and/or jordaning prior. to sheeting the all-mercerized cosity, of the fiber.

pulp may be treated as follows;

pulp furnish is of marked value in the xanthating or other esterifying process, as the smaller cellulose units are reacted upon to completion in a shorter period of time. In the case of chemical wood pulps, such as sulphite pulp, derived from spruce, which have been converted into uniformsheets by my process, thefiber units in the sheets may have an average fiber length of as low as 0.2 to 0.5 mm., or ranging between about 0.2 to 1.0 mm., as against an average fiber length of about 1.5 mm. in the original pulp. This perhaps best shows why xanthation, for example, can be completely effected sooner than in the usual viscose process, wherein sheets of unbeaten pulp serve as raw material.

I have herein spoken about the solution vis- The term solution viscosity as applied to cellulose fiber is an arbitrary one, indicative of the viscosity of a cellulose derivative solution preparable therefrom. The soof fiber in a cuprammonium solution composed of 225 cc. of 28% ammonia water containing 9 grams of cuprous oxide. The C. GrS. is employed because it is definite, denoting a-viscosity 100 times that of water at 20 0., wherefore a cuprammonium cellulose solution of standf ard composition identifying a fiber as vhavingja solution viscosity of 10 is'1000 times as viscous as water at 20 C. Glycerine, which is often referred to when dealing with solution viscosity of cellulose fiber, has a value of between-8 and 10 units.

Examples of procedure falling within the purview of the present invention may be practiced substantially as follows:

Example l.-An unbleached, ordinary sulphite The fiber may be first chlorinated with chlorine watercontaining from 2% to 3% chlorine, based on pulp, at ordinary temperatures. The chlorinated stock, after washing, may then be subjected to the action of an 18% caustic soda solution at 20 C. for from 10 to minutes. If a product of low solution viscosity is desired, I may have present in the caustic soda solution a suitable amount, say-4% to 8% of sodium hypochlorite bleach or other oxidant, based on pulp. The product, at the end of such a treatment, is white and 1138311 alpha-cellulose content of about 97% to 98%. If bleach is present during the alkaline treatment, the solution viscosity of the product will be as .low as .5. If the oxidizing agent is omitted, the

the presence of free alkali, such-as caustic soda.

The final bleached productis thoroughly washed and antichlored. It may then be shortened in fiber length as by meansv of a sharp-bladed Jordan and converted into sheet form on a cylinder machine or on a paper machine equipped with a Fourdrinier wire as the instrumentality on which the pulp is sheeted. Care should be taken to avoid stretches of unsuppported sheet, particularly when it is in wet form.

Example I I.I may vary the procedure, as outlined in Example I, by using a more dilute caustic at lower temperatures. For instance, I may use a temperature of say, 0 C., with a 5% to 6% caustic solution. In this case also, I may use oxidants, as may seem best.

Example III.-If a product of low solution viscosity is not particularly desired, I may use a solution of both caustic soda and sodium sulphide for mercerizing the stock. When this is done, it is necessary to use higher concentration of caustic soda and sodium sulphide, as sodium sulphide is less active as a mercerizing agent than is caustic soda. Low temperatures, such as 0 C., are of advantage in this case. It is evident that no oxidants can be used in conjunction with sodium sulphide on account of the fact that sodium sulphide is a reducing agent and would react with the oxidant.

Example IV.-The procedure may be practiced advantageously in some cases with an unbleached fiber which has not been pretreated with chlorine water and which is not intended to be postbleached. For instance, kraft pulp may be treated merely with a mercerizing liquor and then converted into sheet form as hereinbefore described.

I claim:

1. A process which comprises mercerizing cellulose pulp in bulk form, suspending the mercerized pulp in hot water to inhibit a bunching of fibers, and depositing the fibers from said suspension as a uniformly textured, interfelted sheet.

2. A process which comprises mercerizing cellulose pulp in bulk form, washing the mercerized pulp, beating the mercerized pulp in water until the fibers are reduced markedly in fiber length and become substantially homogeneously suspended as substantially individualized fiber units in the aqueous medium, forming the beaten, mercerized pulp into an interfelted sheet devoid of ingredients other than said mercerized pulp, and converting such sheet into a cellulose derivative while in sheet form.

3. A process which comprises treating preliberated cellulose pulp with a mercerizing liquor under conditions to raise the alpha cellulose content of such pulp to upwards of about 96%, washing the mercerized pulp, beating the mercerized pulp in water until the fibers are reduced markedly in fiber length and become substantially homogeneously suspended as substantially individualized fiber units in the aqueous medium, forming the beaten, mercerized pulp into an interfelted sheet devoid of ingredients other than said mercerized pulp, and converting such sheet into a cellulose derivative while in sheet form.

4. A process which comprises treating preliberated cellulose pulp with a mercerizing liquor containing an oxidant under conditions to raise the alpha cellulose content of such pulp to upwards of about 96% and to lower its solution viscosity to downwards of about 0.6, washing the resulting mercerized pulp, forming the washed, mercerized pulp into a homogeneous suspension of substantially individualized fiber units, and forming an interfelted sheet substantially devoid of ingredients other than said mercerized pulp.

5. As an article of manufacture, a uniformly textured, waterleaf paper sheet made from only bulk, drastically cut, substantially uniformly mercerized cellulose fibers previously substantially uniformly suspended in water as substantially individualized fiber units, as the paper-making material, said sheet being capable of undergoing substantially uniform esterification throughout and said fiber having a solution viscosity of less than 0.5.

6. As an article of manufacture, a uniformly textured, waterleaf paper sheet made from only bulk, drastically cut, substantially uniformly mercerized cellulose fibers previously substantially uniformly suspended in water as substantially individualized fiber units, as the paper making material, said sheet being capable of undergoing substantially uniform esterification throughout and said fiber having an alpha cellulose content of upwards of about 96%.

7. As an article of manufacture, a uniformly textured, waterleaf paper sheet made from only bulk, drastically cut, substantially uniformly mercerized cellulose fibers previously substantially uniformly suspended in water as substantially individualized fiber units, as the papermaking material, said sheet being capable of undergoing substantially uniform esterification throughout and said fiber having an alpha cellulose content of about 96% and a solution viscosity of less than 0.6.

8. The process which comprises substantially uniformly mercerizing cellulose fibers, forming from such mercerized fibers a substantially homogeneous suspension of substantially individualized fiber units substantially all of which have been mercerized, and forming the fibers into a sheet substantially devoid of ingredients other than said fibers.

9. The process which comprises substantially uniformly mercerizing cellulose fibers, forming from such mercerized fibers a substantially homogeneous suspension of substantially individualized fiber units substantially all of which have been mercerized, forming the fibers into a sheet substantially devoid of ingredients other than said fibers, and converting such sheet into a cellulose derivative while in sheet form.

10. As an article of manufacture a substantially uniformly textured waterleaf paper sheet made from substantially only bulk, drastically out, substantially uniformly mercerized cellulose fibers previously substantially uniformly suspended in water as substantially individualized fiber units, as the paper-making material, said sheet being capable of undergoing substantially uniform esterification throughout.

GEORGE A. RICHTER. 

